在多对多表中缺少合适的索引是一个重要的性能问题。遵循中的建议
http://mysql.rjweb.org/doc.php/index_cookbook_mysql#many_to_many_mapping_table
上面写着
这样做吧(当然，要根据特定的表名和列名进行调整。）

CREATE TABLE XtoY (
    # No surrogate id for this table
    x_id MEDIUMINT UNSIGNED NOT NULL,   -- For JOINing to one table
    y_id MEDIUMINT UNSIGNED NOT NULL,   -- For JOINing to the other table
    # Include other fields specific to the 'relation'
    PRIMARY KEY(x_id, y_id),            -- When starting with X
    INDEX      (y_id, x_id)             -- When starting with Y
) ENGINE=InnoDB;

笔记：

⚈  Lack of an AUTO_INCREMENT id for this table -- The PK given is the 'natural' PK; there is no good reason for a surrogate.
⚈  "MEDIUMINT" -- This is a reminder that all INTs should be made as small as is safe (smaller ⇒ faster). Of course the declaration here must match the definition in the table being linked to.
⚈  "UNSIGNED" -- Nearly all INTs may as well be declared non-negative
⚈  "NOT NULL" -- Well, that's true, isn't it?
⚈  "InnoDB" -- More effecient than MyISAM because of the way the PRIMARY KEY is clustered with the data in InnoDB.
⚈  "INDEX(y_id, x_id)" -- The PRIMARY KEY makes it efficient to go one direction; this index makes the other direction efficient. No need to say UNIQUE; that would be extra effort on INSERTs.
⚈  In the secondary index, saying just INDEX(y_id) would work because it would implicit include x_id. But I would rather make it more obvious that I am hoping for a 'covering' index.

要有条件地插入新链接，请使用iodku
请注意，如果您在这个表中有一个auto\ increment，iodku将非常迅速地“烧录”id。